The present invention relates to improvements in electron-beam welding and, more particularly, to a method for checking and stabilizing the depth of fusion in electron-beam welding and a device for effecting same. The invention may be used to the best advantage for controlling and stabilizing the fusion depth in the course of welding metal and metal alloy articles of small and medium thickness with the aid of low-voltage welders having a power of 15 to 20 kw at an acceleration voltage of 50 to 60 kV.
It is highly important to obtain information as to the quality of welding, in particular, the fusion depth, directly in the course of welding. This is equally important from the viewpoint of controlling the welding process and from the viewpoint of locating faulty fusion in order to eliminate the defects found in the weld by way of rewelding. At present, however, there is no method for taking direct measurement of the fusion depth in the course of welding, which would be suitable for checking and control without affecting the weld.
Numerous studies carried out in the past have been aimed at finding indirect parameters of the welding process correlated with the depth of fusion.
One case deals with the research aimed at revealing interrelation between the fusion depth and secondary electron emission currents resulting from electron bombardment of the material being welded.
Also known is a method, whereby pressed to a preset depth into a weld is a material different from that of the article being welded. In the course of welding, investigation is made, with the use of spectroscopic methods, of vapours originating in the welding zone; the moment of the appearance in the spectrum under investigation of lines corresponding to spectral lines of the pressed-in material is indicative of the depth of fusion. Attempts have also been made to determine the fusion depth with the use of X-rays resulting from deceleration of the welding electron beam in the weld crater. This method, however, turned out to be impracticable in the case of welding articles made of X-ray-absorbing materials.
All the foregoing methods have proven to be unsatisfactory due to their complexity, low accuracy and multisided interrelation between parameters affecting the readings of instruments.
More widespread is a method for controlling the depth of fusion, which is based on counting the number of electrons in the electron beam that pass through the weld. This method is applicable when there is access to the weld on the side opposite to the direction of the electron flow. In addition, it is applicable in cases of complete or almost complete fusion of articles being welded. In most cases, however, this method proves to be impracticable due to the foregoing limitations.
It is an object of the present invention to ensure control of the fusion depth directly in the course of welding in cases of both partial and complete fusion of an article being welded.
Another object of the present invention is to simplify the method for controlling the fusion depth.
Still another object of the invention is to increase the accuracy of controlling the fusion depth.
Other objects of the invention include raising the reliability of fusion depth control.